Lumbar disc herniation (LDH) is considered one of the most recognizable and clinically challenging sources of low back pain (LBP). The clinical picture of LDH in the early stages (i.e. the prodromal phase), in which LBP progresses to radicular leg pain and possible neurologic signs, is often uncertain and can be a confusing time. People with LDH may consult a healthcare provider at different points in time along this course before radiculopathy or neurologic deficit has manifested, in which case the treatment itself might be mistakenly blamed for causing the LDH (which, in theory, was going to happen anyway). This type of error is called protopathic bias, wherein reverse-causality bias is present that is related to processes that occur before an outcome has been measured or diagnosed.

The objective was to compare the associations between PCP and chiropractic care in relation to acute LDH with early surgery, while the hypothesis was that chiropractic care could only be thought to increase the risk for acute LDH if the measured association between chiropractic visits and acute LDH exceeded the association between PCP visits and acute LDH.

Following the exclusions process, 195 cases of acute LDH requiring an emergency department (ED) visit and early surgery met the case definition criteria and were included in the analysis:

Seventy-two (37 per cent) of the 195 cases had visited a chiropractor during the 12 month period prior to their event index date, while 186 (95 per cent) had visited a PCP within that same time period.

There were positive associations between chiropractic visits and acute LDH with early surgery regardless of the length of the risk period. For the risk period 0-7 days after a chiropractor visit, the adjusted incidence rate ratio (IRR) was 12.9 (95 per cent CI 7.2-23.3).

There were also strong positive associations between PCP visits and acute LDH with early surgery for all risk periods. The risk period 0-7 days after a PCP visit resulted in an IRR of 14.5 (95 per cent CI 9.9-21.2).

When the analyses were restricted to only include visits related to lumbar spine complaints, the associations for PCP visits increased, but not associations for chiropractic visits.

Sensitivity analyses were performed, which essentially did not change the above results.

A bootstrap analysis of the ratio of the incidence rate ratios for chiropractic care compared to PCP care was performed, which showed a positive safety profile for chiropractic care as compared to PCP care.

Applications, conclusionsThe authors concluded that patients with prodromal back pain caused by a developing lumbar disc herniation seek healthcare from both chiropractors and PCPs prior to full clinical expression of acute LDH that is eventually managed with early surgery. The positive associations between PCP visits and acute LDH with early surgery were stronger than for chiropractic care.

Even though a positive association between chiropractic care and acute LDH with early surgery was found in this study, the fact that there was a stronger positive association between PCP visits (which would not plausibly cause LDH) and acute LDH with early surgery suggests that the associations are explained by protopathic bias. In other words, patients with LDH-related LBP may have sought healthcare for this prodromal symptom before the LDH was diagnosed. It is also possible that spinal manipulation or even physical examination manoeuvres could exacerbate a developing or latent disc herniation, leading to full clinical expression of an already-existing condition.

The authors pointed out that there are no clinical screening tests available that can accurately identify LBP patients who are at increased risk of developing acute LDH. They also pointed out that most physical tests used to identify LDH are not very accurate.

Clinicians should therefore continue to be vigilant when caring for patients with LBP, observing for signs and symptoms of neurological involvement and take appropriate actions if they occur.

Dr. Shawn Thistle is a practicing chiropractor, educator, international speaker, knowledge-transfer leader, evidence-based health care advocate, entrepreneur & medicolegal consultant. He founded RRS Education in 2006 and currently acts as the company’s CEO. RRS Education helps chiropractors and other manual medicine clinicians around the world integrate research in to patient care via weekly Research Reviews, Online Courses and Seminars. For more information, visit: www.rrseducation.com.